Submerged nozzle for continuous casting

ABSTRACT

A nozzle for the continuous casting of steel which has at least one outlet below the slag-covered surface of the molten metal in the mold, is protected against corrosive effects of the slag at the surface of the molten metal and also against erosion in the outlet region of the nozzle by refractory rings.

United States Patent Neumann et a]. Apr. 2, 1974 [54] SUBMERGED NOZZLE FOR CONTINUOUS 3,349,838 10 1967 Baier 164/281 CASTING 3,392,888 7/1968 Cahoonct al. 222/566 3,459,346 8/1969 Tinnes 222/566 1 Inventors! Friedhelm Nellmann, Adliswil; Josef 2,938,251 5 1960 Baicr 164/281 ux K. Zeller, Weesen, both Of 3,370,432 2/1968 Butler ct al. 6l/54 Switzerland [73] Assignee: Concast AG, Zurich, Switzerland Primary Examiner Robert D. Baldwin 22 Filed; Sept 1 1970 Attorney, Agent, or Firm-Sandoe, Hopgood &

C l' afd 211 App]. No.: 72,692 a e [30] Foreign Application Priority Data 57] ABSTRACT Sept. 16, 1969 Switzerland 13937/69 A nozzle for the continuous casting of steel which has [52] US. Cl. 164/281 at least one outlet below the slag covered surface of [51] lift. the molten metal in the mold, is protected g i [58] Field of Search 164/281, 337, 281, rosive effects of the slag at the surface of the molten 222/566 D 1*23 573 metal and also against erosion in the outlet region of th 22! b f t [56] References Cited 6 no e y re me my rmgs UNITED STATES PATENTS 5 Claims 6 Drawing Figures 3,050,792 8/1962 Lipman et al 164/281 PMENTEDAPR 2 I914 FIGZ FIG-| SUBMERGED NOZZLE FOR CONTINUOUS CASTING The present invention relates to the continuous casting of steel through a nozzle having at least one submerged outlet through which molten metal is discharged continuously below the slag-covered surface of the molten metal in the mold.

Nozzles with submerged outlets are used in continuous casting plants to prevent oxidation of the steel on its way from the tundish to the mold or from the ladle to the tundish. The use of such nozzles also prevents slag particles and oxides from being washed into the liquid core of the strand.

The increasing weight of individual heats and the introduction of uninterrupted continuous casting have led to a very considerable lengthening of the casting times. This exposes the nozzles of refractory material to considerable wear and the life of these nozzles is a factor that limits the length of the casting times.

If a flux powder is used for covering the surface of the molten metal in the mold, the exterior of the nozzle will show signs of erosion at the level of the surface of the molten metal after relatively short casting times. This is primarily due to the corrosive effect of the slag formed by the powdered flux which is continuously agitated by the movement of the steel in the mold. However, erosion phenomena may appear in the interior of the nozzle in the region of the outlet orifice, particularly when casting manganese alloyed steels. Such erosion phenomena often result in the nozzle breaking off where it has thus been weakened. Such fractures lead to slag being undesirably washed into the liquid core of the strand if the tundish carrying the nozzle is not immediately lowered to re-immerse the end of the nozzle below the metal level. Moreover, in the case of nozzles provided with lateral outlets an adverse pattern of flow in the liquid core of the strand involving the deeper strata, occurs when the portion of the nozzle that dips into the molten metal breaks away. Particularly in curved mold casting plants, changes in the pattern of flow result in erosion of the frozen shell of the casting, increasing the risk of breakout as well as the tendency for cracks to be formed in the casting.

The object of the present invention is to reduce the exterior erosion of the nozzles caused by chemical and physical action of the slag at the surface of the molten metal and to compensate for erosion in the interior of the nozzles in the region of the nozzle outlet to prolong the life of such submerged nozzles.

According to the present invention, this is achieved by concentrically locating a separate ring of refractory material around the nozzle. This ring extends downwards below the surface of the molten metal and upwards above the surface of the layer of slag.

To protect the nozzle from the erosive action of the slag when the mold metal level varies and also to facilitate the replacement of the ring, it is advantageous to let the ring float on the molten metal. The inside diameter of the ring may exceed the outside diameter of the nozzle by at least 2 mm.

To prevent the ring from sinking below the nozzle end when the mold metal level drops considerably, and also to facilitate the start-up, the nozzles may be provided with protrusions which restrict the downward movement of the floating ring.

Any desired depth of immersion of the ring can be obtained regardless of its specific weight by fixing the ring in a position which is determined by the desired mold metal level. The ring may thus be located by stops on the nozzle.

When used with a nozzle having lateral outlets, the ring surrounds the outlet openings of the nozzle extending vertically downward from above the openings, to provide support for the wall of the nozzle and to compensate for'the effects of erosion in the outlet area. The ring, which may be threaded or otherwise secured to the nozzle, has openings which register with the nozzle outlet openings.

Embodiments of the present invention will be described in greater detail with reference to the accompanying drawings in which FIG. 1 is a vertical section of part of a tundish fitted with a nozzle that extends below the level of the molten metal in the mold.

FIG. 2 is a vertical section of the end of an alternative form of nozzle.

FIG. 3 is a section taken on the line III-III OF FIG. 2.

FIG. 4 is a section of the lower end of another form of nozzle.

FIG. 5 is a section of the lower end of yet another form of nozzle.

FIG. 6 is a section taken on the line VIVI of FIG. 5.

Referring to FIG. 1, the floor of the tundish l is fitted with a tubular nozzle 2 which has an outlet below the surface 3 of the molten metal in a continuous casting mold 4. The surface 3 of the molten metal is covered with slag 5 from a flux powder scattered on the surface of the molten metal. A ring 6 of refractory material which is substantially concentric with the nozzle floats on the surface 3 of the molten metal and protects the nozzle surface from chemical and physical erosion caused by the slag 5. Sufficient clearance is provided to allow the floating ring to rise or fall freely as the level of the molten metal changes. The extent to which the ring 6 will be immersed below the surface of the molten metal will depend on its specific gravity. In order to protect the nozzle surface from the corrosive layer of slag even above the layer of slag, the ring 6 preferably extends above the layer of slag 5 a distance that is usually several times the thickness of the layer of slag.

If desired, spare rings 6,6" may be mounted on the nozzle 2 before casting begins to serve as replacements, should the ring 6 be destroyed by wear. Retaining means 7 which are shown schematically, hold the spare rings 6,6" above the level of the molten metal and layer of slag until they are needed.

FIG. 2 shows a form of nozzle 12 having two lateral outlet openings 13 below the level 3 of the molten metal. As in FIG. 1, a refractory ring 14 floats on the surface 3 of the molten metal. Preferably the inner corners l5 and 16 of the ring 14 are rounded, and the inner surface 19 of the ring is curved convexly to facilitate sliding and to prevent jamming between the nozzle and the ring. The clearance 20 between the nozzle and the ring should be at least 2 mm.

Stops 17 in the form of bosses located below the level of the molten metal, prevent the ring from slipping off the nozzle 12, should the surface of the molten metal drop accidentally. Spare rings 14' and 14' rest on stops l7 and 17".

FIG. 3 shows the stops 17 in section. They form bayonet joints with the recesses 18 in the rings l4, l4 and 14". The rings can thus be slid over the stops 17, 17 and 17" and are then turned by an angle of about 90 to become supported and retained by the next lower stop.

In FIG. 4 a ring 46 is mounted on a nozzle 2 which is provided with bosses 42 and 43 located, respectively, below and above the ring and which retain the ring in a predetermined location in relation to the desired mold metal level 3. Ring 46 may, if desired, be provided with recesses similar to the recesses 18 of FIG. 3 to permit the ring to be moved up or down if necessary.

FIG. 5 shows a nozzle 12 which has threads 53 and two lateral outlets 13. the ring 54 is threaded to the nozzle 12 and may be adjusted to a predetermined position in respect to the desired mold metal level 3. The nozzle 2 may also have only one lateral outlet opening 13. The ring 54 protects the exterior of the nozzle from the erosion by the slag 5 and also compensates for the interior erosion indicated by dashed lines 57 in the outlet region of the nozzle 2, which is particularly pronounced during longer casting times when casting manganese alloyed steels. Should the nozzle 12 fracture because of major erosion, for example along an assumed line 58, then the broken part of the nozzle 12 is held in its former location by the threaded ring 54 which also counteracts the dynamic flow forces which act in the direction of the nozzle axis. Casting can therefore continue without any change in the flow conditions.

If desired, the ring 54 may be shaped like a cup, having a horizontal bottom part to provide additional protection against a vertical metal break-through at the bottom of the nozzle 12.

FIG. 6 shows a horizontal cross section of the nozzle 12 and of the ring 54 taken on the line VI--VI in FIG. 5. The outlet openings 59 in the ring 54 match the outlet openings 13 of the nozzle 12. As an alternative to threads, other means of attachment, such as a bayonet joint, may be used to keep the ring in the desired location against forces acting in the longitudinal axis of the nozzle.

the rings 6, 14, 46 and 54 are preferably made of a refractory material which is chemically neutral to the slag. Mixtures of graphite and clay, as are conventionally used for manufacturing nozzles, are quite suitable. Other refractory materials may also be used, but they should be selected with due regard to the composition of the slag and the quality of the steel to be cast. It has been found that the above described rings are exposed to much lower mechanical stresses than the nozzles and can therefore be manufactured of refractory materials with a lower mechanical strength.

The above described nozzles and rings may also be used between the ladle and the tundish. The rings may have an oval or flattened cross section when they are used for casting strands of a small cross section.

We claim as our invention:

1. Apparatus for protecting the inlet nozzle of a continuous casting machine from the corrosive and erosive effects of flux powder slag at the surface of the molten metal during the continuous casting of steel, comprising a casting mold, a tubular nozzle extending into said mold having a discharge outlet adapted to be located below the level of the molten metal and slag in the mold, and a floating refractory ring surrounding said nozzle and concentric therewith, the interior surfaces of said ring being in close sliding relationship with the exterior surfaces of said nozzle and guided thereby but having clearance to permit said ring to rise and fall with changes in the level of the molten metal in the mold while preventing access of flux powder slag to the exterior of the nozzle during said rise and fall, said ring being adapted to extend downwardly below the level of the molten metal, and being adapted to extend upwardly above the level of the slag.

2. Apparatus according to claim 1 in which the inside diameter of said ring exceeds the outside diameter of said nozzle by at least 2 mm.

3. Apparatus according to claim 1 in which said nozzle is provided with stops which restrict the downward movement of said ring.

4. Apparatus according to claim 1 in which the nozzle is provided with means whereby movement of said ring on said nozzle is restricted in both directions.

5. Apparatus according to claim 4 in which said nozzle is provided with stops which restrict the downward movement of said ring, and additional stops which restrict the upward movement of said ring. 

1. Apparatus for protecting the inlet nozzle of a continuous casting machine from the corrosive and erosive effects of flux powder slag at the surface of the molten metal during the continuous casting of steel, comprising a casting mold, a tubular nozzle extending into said mold having a discharge outlet adapted to be located below the level of the molten metal and slag in the mold, and a floating refractory ring surrounding said nozzle and concentric therewith, the interior surfaces of said ring being in close sliding relationship with the exterior surfaces of said nozzle and guided thereby but having clearance to permit said ring to rise and fall with changes in the level of the molten metal in the mold while preventing access of flux powder slag to the exterior of the nozzle during said rise and fall, said ring being adapted to extend downwardly below the level of the molten metal, and being adapted to extend upwardly above the level of the slag.
 2. Apparatus according to claim 1 in which the inside diameter of said ring exceeds the outside diameter of said nozzle by at least 2 mm.
 3. Apparatus according to claim 1 in which said nozzle is provided with stops which restrict the downward movement of said ring.
 4. Apparatus according to claim 1 in which the nozzle is provided with means whereby movement of said ring on said nozzle is restricted in both directioNs.
 5. Apparatus according to claim 4 in which said nozzle is provided with stops which restrict the downward movement of said ring, and additional stops which restrict the upward movement of said ring. 